Portable Document Format (PDF) is an open standard for document exchange. The file format can be used for representing two-dimensional documents in a manner independent of the application software, hardware, and operating system. Each PDF file encapsulates a complete description of a fixed-layout 2D document that includes the text, fonts, images, and 2D vector graphics which compose the documents. In some examples, three-dimensional drawings can be embedded in PDF documents. PDF files can be comprised of objects such as Boolean values, numbers, text strings, etc. Objects of a PDF file can be either direct (embedded in another object) or indirect. Indirect objects can be numbered with an object number and a generation number.